Field
The present disclosure relates to the field of lithium-ion batteries, and more specifically, to an overcharging preventive electrolyte and lithium-ion battery.
Background
As most of current lithium-ion batteries use carbonate ester organic electrolytes that are extremely flammable, overcharging, over-discharging, and overheat of the batteries could all likely cause the batteries to burn or even explode. Given that fundamental changes to electrode materials, electrolyte materials, and separator materials are unlikely to happen for the foreseeable future, improving the stability of electrolyte is an important way to improve the safety of lithium-ion batteries.
Overcharging preventive electrolytes of lithium-ion batteries are categorized mainly into two types: the electro-polymerization type and the REDOX type. Although the electro-polymerization type additives, such as biphenyl and cyclohexylbenzene, can effectively inhibit battery overcharging, the addition thereof will damage the cycle performance of a battery. On the other hand, even though the REDOX type additives, such as ferrocene and derivatives thereof, anisyl benzene and derivatives thereof, etc., have reversible overcharging protection mechanisms, due to the relatively low oxidation potential thereof, redox reaction takes place before the normal operating voltage (e.g., 4.2 V) of a lithium-ion battery is reached. This often restricts the large-scale applications of the REDOX type additives in lithium-ion batteries of different battery material systems. WO Publication No. WO2008138132A1 published on Nov. 20, 2008 discloses application examples in which nitrile compounds are used as solvents or additives for electrolytes of lithium-ion batteries, and describes the prospect of nitrile compounds being used as solvents for electrolytes. Nitrile compounds, such as glutaronitrile and adiponitrile, have an electrochemical window up to 8.3 V (vs Li/Li+), which is wider than the electrochemical windows of all aprotic solvents, including sulfones, and have the advantages of good thermal stability, low viscosity, and high dielectric constant. However, the compatibility between nitrile compounds and low-potential cathodic active materials for lithium-ion batteries, such as graphite or metal lithium, is relatively poor. It is very easy for polymerization reaction to take place on the surface of cathode. The polymerization products will block the de-intercalation of Li+, which affects the cycle performance of lithium-ion batteries.